1. Field of the Invention
The present invention relates to a variable geometry boat hull and more particularly to a boat hull which incorporates the air cushion principle.
2. Description of the Prior Art
Air cushion vessels fall into two general categories. Full skirted vessels have a non-rigid, inflatable, skirt which surrounds the vessel and entrains air beneath the hull. Solid side wall vessels on the other hand have solid side wall portions which engage, and project into, the water, while having flexible, inflatable, air entrainment barriers at least at the stern of the vessel and extending between the two solid side walls. In some cases air entrainment means will also be provided at the bow of the vessel and again extending between the solid side walls.
The solid side wall vessels have a number of substantial advantages as compared with the fully skirted vessels. The solid side walls more effectively entrain the air beneath the vessel and therefore less energy is needed to maintain the cushion of air beneath the vessel. Further energy savings are provided by the lower energy requirement in order to maintain the air entrainment means inflated. The solid side wall vessels have also been found to have better seakeeping qualities which makes them advantageous for long journeys in open water.
The full skirted vessels, however, have a significant advantage in that they are able to move on land which is not generally possible with the solid side wall version.
To overcome the problems associated with solid side walls retractable seals which can be called upon when needed have been proposed. Two such seal arrangements are known; one whereby recess is formed in each side wall to accommodate an inflatable extendable seal whilst the other arrangement is to fit a flap type mechanism against the insides of each side wall which can be pivoted up and held or pivoted down to extend below the sides of the hulls.
Both types of air cushion vehicle (fully skirted or solid sidewalled) do not have ability to travel at speed except when supported on an air cushion and in this state both are limited in their sea going capability.
Both types of air cushion vehicle are dependent upon air propulsion for travel out of the water.